1. Field of the Invention
The present invention relates to a display device, and more particularly, to a display device increasing a driving frequency of a display image in order to improve performance for displaying moving image.
2. Description of the Related Art
In view of displaying moving image, display devices are roughly categorized into impulse type display devices and hold type display devices. The impulse type display device, typified by a cathode ray tube display device, is of a type in which brightness of scanned pixels is increased only for period for the scanning and is decreased immediately after the scanning. The hold type display device, typified by a liquid crystal display device, is of a type that continues to keep brightness based on display data until next scanning.
The hold type display device advantageously obtains excellent display quality without flicker when displaying still image, but has a problem that when displaying moving image, a periphery of a moving object appears to be blurred, that is, so-called motion blur occurs to decrease display quality significantly. The reason why the motion blur occurs is due to a so-called retinal after-image, which is a phenomenon that, when an observer moves his/her line of sight along with the motion of the object, the observer interpolates display images before and after the motion with respect to a display image whose brightness is held. Therefore, even if a response speed of the display device is improved as much as possible, the motion blur cannot disappear completely.
As one of the known measures against such a problem, Japanese Patent Application Laid-open No. Hei 04-302289 discloses a technology of interpolating sub-frame images so that a frame frequency of a display image may be increased to resolve the above-mentioned motion blur (nx-speed drive). However, a response speed of liquid crystal greatly depends on temperature, and in particular under low temperature, the input signal following capability is extremely deteriorated to increase response time. If internal temperature of the device is low, a subsequent sub-frame image starts to be written before the liquid crystal responds completely to obtain target brightness. As a result, there arises a more severe problem that an after-image, such as tailing, occurs to cause image quality degradation in the display image.
As measures against the problem, Japanese Patent Application Laid-open No. 2004-177575 discloses a display device for controlling a frame frequency conversion rate of a liquid crystal display panel in accordance with internal temperature of the device.
Further, as another method of reducing the motion blur, for example, Japanese Patent Application Laid-open No. 2000-321551 discloses a technology in which a plurality of direct type backlights are arranged on a rear surface of a liquid crystal display panel in a direction parallel to scanning lines and are sequentially flashed in synchronization with scanning signals so that display characteristics of the display device may be obtained similar to those of the impulse type (hereinafter, referred to as scanning type intermittent lighting drive).
Further, Japanese Patent Application Laid-open No. 2004-45748 discloses displaying a part of a screen in a liquid crystal display device and not displaying the other area of the screen mainly for reducing power consumption associated with the displaying (partial drive).